1. Field of the Invention
The present invention relates to image forming apparatuses, image forming system, and image forming methods.
2. Description of the Related Art
Printers including, for example, an image bearing body for bearing a latent image, a developer bearing body that bears a developer and that is for developing the latent image borne on the image bearing body with the developer, and a transferring section that transfers, onto a medium to form an image thereon, a developer image formed on the image bearing body by the development of the latent image, are known as one type of image forming apparatus. Such a printer also has a voltage applying section that alternately applies, to the developer bearing body, a first voltage for making the developer move from the developer bearing body toward the image bearing body in order to develop the latent image, and a second voltage for making the developer move from the image bearing body toward the developer bearing body. It should be noted that developers having different charge amounts are borne on the developer bearing body by means of, for example, image force. (See, for example, JP 2002-182457A.)
(1) Further, the printer of the above-mentioned type has an image darkness adjusting section for adjusting the darkness of an image to be formed on the medium. The image darkness adjusting section of the conventional type adjusts the darkness of an image to be formed on a medium by changing the first voltage (also referred to as “Vmax”) and the second voltage (also referred to as “Vmin”). In doing so, there are cases in which the absolute value of the first voltage becomes small.
If the absolute value of the first voltage is too small, then the force for making the developer move from the developer bearing body toward the image bearing body would be insufficient, and thus, it may not be possible to move some of the highly-charged developer from the developer bearing body toward the image bearing body (this is a phenomenon called “selective development”). Furthermore, in such a case, the highly-charged developer, which has not moved toward the image bearing body, remains borne on the developer bearing body; thus, it becomes difficult for the developer bearing body to bear some new developer.
(2) Further, in the printer of the above-mentioned type, the developer bearing body is arranged in opposition to the image bearing body with a gap therebetween, and the printer further includes an image darkness adjusting section for adjusting the darkness of an image to be formed on the medium. In consideration of preventing the above-mentioned phenomenon (the so-called “selective development”) in which a portion of the developer borne on the developer bearing body does not move toward the image bearing body, it is effective to adjust the darkness of an image by fixing the first voltage (“Vmax”) at a large absolute value, and changing only the second voltage (“Vmin”).
However, if the darkness of an image is to be adjusted simply by changing only the second voltage, then the second voltage could take a wide variety of values. If the absolute value of the second voltage is too large, then the difference between the electric potential of the developer bearing body caused by the second voltage and the electric potential of the image bearing body will be too large, which may give rise to electric discharge. On the other hand, if the absolute value of the first voltage is too large, then the difference between the electric potential of the developer bearing body caused by the first voltage and the electric potential of the image bearing body will be too large, which may also give rise to electric discharge.
(3) Further, as described above, the printer of the above-mentioned type has an image darkness adjusting section for adjusting the darkness of an image to be formed on the medium. In consideration of preventing the above-mentioned phenomenon (the so-called “selective development”) in which a portion of the developer borne on the developer bearing body does not move toward the image bearing body, it is effective to set the absolute value of the first voltage to a large value.
However, if the absolute value of the first voltage is too large, then the amount of developer that flies from the developer bearing body toward the image bearing body will increase. This increase may give rise to an increase in fogging or scattering of developer.
(4) Further, in the printer of the above-mentioned type, the developer bearing body bears the developer, carries the developer to a position that is in opposition to the image bearing body, and develops the latent image borne on the image bearing body with the developer that has been carried up to that position, and the printer further includes an image darkness adjusting section for adjusting the darkness of an image to be formed on the medium. In consideration of preventing the above-mentioned phenomenon (the so-called “selective development”) in which a portion of the developer borne on the developer bearing body does not move toward the image bearing body, it is effective to adjust the darkness of an image by changing only the second voltage (“Vmin”), among the first voltage (“Vmax”) and the second voltage.
However, if the darkness of an image is to be adjusted simply by changing only the second voltage, then the second voltage could take a wide variety of values; in that case, depending on the value of the second voltage, darkness non-uniformities may appear in the image. On the other hand, if the absolute value of the first voltage is too large, then this may give rise to an increase in fogging or scattering of developer.